A prior art supply circuit is known from U.S. Pat. No. 5,668,464, which discloses a feed forward active filter for output ripple cancellation in switching power converters. The prior art switching power converter comprises an inductor. A first side of the inductor is coupled to a switch and a second side of the inductor is coupled to a parallel circuit of a capacitor and a load. The switching of the switch results in a ripple voltage present in the output voltage across the capacitor. To compensate for this ripple voltage, the prior art switching power converter comprises complex circuitry for detecting the ripple voltage and for deriving a compensating current from the detected ripple voltage. This complex circuitry comprises for example two integrators, two multipliers and an amplifier. The prior art switching power converter further comprises a transformer for injecting the compensating current into the parallel circuit of the capacitor and the load.
The known supply circuit is disadvantageous, inter alia, owing to the fact that it comprises a resonant injection circuit that may interfere with the load. Further, in case of the load introducing much noise across the capacitor, the ripple voltage might be difficult to detect across this capacitor.